The deployment manager that scans for and deploys webapps and contexts.

Login services that provide authentication checking.

A request log.

Not all Jetty features are configured in jetty.xml.
There are several optional configuration files that share the same format as jetty.xml and, if specified, concatenate to it.
These configuration files are also stored in $JETTY_HOME/etc/, and examples of them are in Github Repository.
The selection of which configuration files to use is controlled by start.jar and the process of merging configuration is described in Jetty XML Usage.

Root Element

jetty.xml configures an instance of the Jetty org.eclipse.jetty.server.Server.